Production of amidine salts



Patented Aug. 5, 1947 PRODUCTION OF AMIDINE SALTS Harry James Barber, Gidea Park, Romford, England, assignor to May & Baker Limited, Dagenham, England, a British company N Drawing.

Original application August 27,

1943, Serial No. 500,293. Divided and this application February 15, 1945, Serial No. 578,115. In Great Britain July 27, 1942 6 Claims.

Thi invention is for improvements in or relating to the preparation of amidine salts, especially salts of diamidines of the aromatic series. This is a division of my co-pending application Serial No. 500,293, filed August 27, 1943.

The most commonly known amidine salts, the hydrochlorides, have usually been prepared by treating the corresponding nitrile with anhydrous alcoholic hydrochloric acid to form the corresponding imino-ether hydrochloride which has then been converted into the amidine hydrochloride by treatment with ammonia. In the case, for example, of the di-hydrochlorides of diamidines, especially diamidines 0f the aromatic series, it was found necessary to employ large excess quantities of anhydrous hydrochloric acid in order to cause the conversion of the nitrile into imino-ether hydrochloride to proceed at a reasonable speed and to completion. This frequently led to difiiculties as it was necessary to remove at least the greater part of the excess of acid in order satisfactorily to carry out the next stage (conversion of imino-ether hydrochloride into amidine hydrochloride). Thus, when the conversion of nitrile to imino-ether hydrochloride was carried out in a diluent, and this hydrochloride did not separate, it was necessary to pump ofi considerable quantities of hydrochloric acid gas, which is objectionable for industrial scale operation.

Even when the imino-ether hydrochloride did separate, it often contained considerable quantitles of free hydrochloric acid which was removable but slowly. For this reason and since also these imino-ether hydrochlorides are unstable, being decomposed by alcohol, it has been necessary to use a considerable excess of anhydrous alcoholic ammonia (e. g., 10 molecules of ammonia for each imino-ether group) for the step of converting the imino-ether hydrochlorides into the corresponding amidine hydrochlorides.

The production of other amidine salts than the hydrochlorides has involved the same difiiculties since these other salts have hitherto been prepared either directly from the hydrochloride or from the amidine base, itself prepared from the hydrochloride.

It has now been discovered that the foregoing disadvantages are avoided if, instead of converting the imino-ether hydrochlorides directly into the corresponding diamidine hydrochlorides, the imino-ether hydrochlorides are converted into the corresponding imino-ether bases and the latter then treated with an ammonium salt. By workin in this way, it is possible to obtain not 2 only amidine hydrochlorides but also any other desired amidine salt. The imino-ether bases are more stable than their hydrochlorides and in many cases are well-defined, crystalline substances which may be rte-crystallised from a number of organic solvents. I

The process of the present invention for the production of amidine salts of an'acid therefore comprises causing reaction between an iminoether base (corresponding to the-amidine) and an ammonium salt of the said acid thereby to produce the amidine salt of the said acid.

t should be understood that the expression imino-ether base corresponding to the amidine as used in this specification and in the appended claims includes any imino ether having the formula of the amidine in question in which the amidine radical C( 'NH)NH2' is replaced by the imino-ether radical (C=NI-I) OR where R is any desired substituent for V example a methyl, ethyl or p-phenylethyl radical.

This process is particularly applicable to the production of salts of aromatic diamidines having the general formula Am.B.X.B.Am wherein Am represents the amidine group, B represents an aromatic nucleus and X represents: (a) a direct linkage, or (b) an alkane chain (CHZM where n is an integer from 1 to 12 in which one or more of the CH2 groups may be replaced by an oxygen or sulphur group or an NH group, or (c) a 'CR1=CR2-- group in which R1 and R2 may be the same or different and represent hydrogen atoms or alkyl,'aralkyl or aryl groups. Diamidines of this type are described in United States Patents Nos. 2,277,861 2,277,862 and 2,20%,983 and application S. N 0. 426,603.

The imino-ether bases employed as-starting material may be obtained from their hydrochlorides (prepared in' conventional manner). Thus, for example, the crude imino-ether hydrochlorides of the class corresponding to the aromatic diamidines having the foregoing general formula can be readily converted to the free imino-ether bases by suspending them in an inert solvent (chloroform is particularly suitable) and. then adding, with good stirring and adequate cooling, e. g., by the addition of crushed ice, sufficient aqueous caustic soda solution to make the reaction mixture alkaline to phenolphthalein; The free base liberated, rapidly dissolves in the chloroform layer, which-is separated from the aqueous layer and is thereafter washed and dried. The free bases obtained on evaporation of the chloroform are, in many cases, well-defined crystalline substances, which may be recrystallised from a number of organic solvents, of which benzone has been found most generally suitable.

It is not, however, essential to isolate the imino-ether hydrochloride (even in the crude state) before converting it into the imino-ether base. Thus, the imino-ether base can be obtained from the reaction mixture resulting from the usual process of preparing the hydrochloride (i. e., by saturating a solution or suspension of the nitrile, containing an anhydrous alcohol, with dry hydrochloric acid gas, and allowing to stand for the time required to complete the reaction) by treating this reaction mixture in the manner described above for the crude imino-ether hydrochloride. When, as is sometimes thecase, the said anhydrous alcohol is employed in conjunction with an inert solvent, such as chloroform, the imino-ether base can be obtained from the reaction mixture simply by adding, with good stirring, a considerable excess of aqueous caustic soda solution, with cooling by addition of crushed ice. The separation of the free base is effected in the manner described above- In carrying the present invention into eiiect, the imino-ether base obtained in the manner described above may be converted to any amidine salt by treatment with an appropriate ammonium salt, preferably in a suitable solvent medium. It, has been found that the reaction can be carried out quite smoothly in aqueous alcoholic solution or suspension.

Suitable imino-ethers are, for example, those corresponding to the imino-ether hydrochlorides specified in. United States Patents Nos. 2,277,861, 2,277,862 and 2,204,983 and application Ser. No. 426,603. The ammonium salt employed is, of course, that corresponding to the amidine salt desired. Typical examples are ammonium chloride, ammonium beta-hydroxy-ethane sulphonate, ammonium beta-hydroxy-propane sulphonate, ammonium lactate and ammonium methane sulphonate.

It is convenient to dissolve the ammonium salt of. the acid in water and the imino-ether base inv an alcohol such as ethyl alcohol, thev proportions of each being so adjusted that both components remain in solution after mixing at about 50 to 60 C. The amidine salt may or may not. separate from the reaction mixture after some four or five hours, according to the solubility of the amidine salt- If it is soluble, it isconvenient to concentrate to an appropriate degree and to crystallise by the addition of excess alcohol or acetone. The temperature range of 50 to 80 C. is preferred in practice but lower temperatures may also be used. Care should be taken to avoid substantially higher temperatures, i. e., up to boiling point such as would result in the loss from the reaction mixture of any substantial amount of ammonia required for the reaction.

A modification of the process hereinbefore defined and which is within the scope of this invention comprises reacting the imino-ether base with a salt of an organic base. Salts of primary or secondary amines can be employed, for example ethylamine lactate and piperidine hydrochloride.

An important advantage of the present invention lies in its applicability to the production of any amidine salt, whereas procedures hitherto described have yielded only the hydrochlorides from which the other salts have had to be prepared. Moreover, as has already been pointed out, the production of amidine hydrochlorides by the process of the present invention esults inthe elimination of disadvantages hitherto experienced.

The process of the present invention is illus trated by the following example:

Example 16 kilos of 4:4"- dicyanodiphenyl ether in line powder (100 mesh) were suspended in 24 litres of anhydrous chloroform and 9.6 litres of anhydrous ethyl alcohol. Dry hydrogen chloride (6.4 kilos) was then passed in with good stirring, the temperature being maintained below 15 C. by suitable external cooling. The operation was carried out in a, suitable closed vessel fitted with a stirrer and. designed so that moisture was excluded. The vessel was sealed and the temperature allowed to rise to 25 C. A slight pressure was thereby developed, but this sOOn fell as the reaction proceeded. After about 5 days, the reaction mixture was run into crushed ice, and 50% aqueous caustic soda solution (about 30 litres) added until the mixture was permanently alkaline to phenolphthalein; Ice should still be present at the end of this operation. After stirring for some time, the chloroform solution of the diiminoether base was separated and the chloroform distilled off finally under reduced pressure. The residual crude di-imino-ether base was dissolved in 32 litres of ethyl alcohol and a solution of 22 kilos of ammonium isethionate dissolved in 13 litres of hot water added. The mixture was maintained at 45 C. for 24 hours with stirring. The resulting solution was treated with 500 grams of decolourising charcoal and filtered. The clear filtrate was then run into" 100 litres of stirred acetone. The product which crystallised was filtered, washed and dried at 100 C.

I claim:

1. Process for the production of a salt of a symmetrical aromatic diamidine, which comprises reacting a symmetrical di-imino-ether base of the formula:

in which R is a lower alkyl radical, with an ammonium salt of an acid, in an aqueous alcoholic medium, and isolating the resulting 'diamidine' salt from the reaction mixture.

2. Process according to claim 1 wherein the reaction is oonducted at an elevated temperature below that at which any substantial quantity of ammonia is evolved from the reaction mixture.

3. Process according to claim 1 wherein both the ammonium salt ofan acid and the di-iminoether base are soluble in the said medium, and the reaction is conducted at a temperature between 50" and 80 C.

4. Process according to claim 1 wherein the medium is an. aqueous alcoholic suspension, and the reaction is conducted at a temperature between 50 and 80 C.

5. Process according to claim 1 wherein the ammonium salt of an acid is dissolved in water andthe di-imino-ether base is dissolved in an alcohol, the proportions of each being so adjusted that both components remain in solution on the solutions being mixed together at about 50 to 80 C., and thereafter mixing together the two solutions at atemperature within this range.

6. Process for the production of the 4:4- bis(carbonamidine)-di-beta-hydroxyethane sulphonate of diphenyl ether which comprises reacting, in an aqueous alcoholic medium, am-

6 mom'um-beta-hydroxy-ethane sulphonate with Number Name Date 4:4'-bis(carboniminoethy1 ether) diphenylether, 2,277,862 Ewins et a1 Mar. 3 1942 and isolating the said diamidine salt from the FOREIGN PATENTS reaction mixture.

HARRY JAMES BARBER. 5 Number Country Date 116,718 Australia Mar. 12, 1943 REFERENCES CITED 559,015 Great Britain Feb. 1, 1944 The following references are of record in the OTHER REFERENCES me of thls patent: 1O Beilstein, Handbuch der Org. Chem, IV ed.,

UNITED STATES PATENTS v01. IX, p. 271.

Number Name Date Beilstein, IV ed., vol. IX, supp, p. 121 (Knorr,

2,204,983 Ewins June 18, 1940 3501235)- 2,277,861 Ewins et a1. Mar. 31, 1942 

